Despite recent advances in neonatal intensive care, bronchopulmonary dysplasia (BPD) remains a major cause of infant morbidity and mortality. The mechanisms for the development of BPD are multifactorial and not yet clearly defined. Inflammation is a common feature of BPD. Airway inflammation is associated with an influx of inflammatory cells and their products. Neutrophils, macrophages and airway epithelial cells release potent proteinases during the inflammatory cascade. These proteinases are involved in diverse physiologic and pathologic processes, such as extracellular matrix remodeling, angiogenesis, apoptosis and innate immunity. In the healthy lung as well as during normal development, the activity of proteinases are tightly regulated by local and systemic anti-proteinases. Among the local proteinase inhibitors, members of the ov-serpin family (ovalbumin-related serpins) are an emerging group of proteins that are abundantly expressed by several cell types in the lung, including airway epithelial cells, endothelial cells and inflammatory cells. These ov-serpins include SERPINB1, -B2, -B3, -B4, B6 and B9. Ov-serpins inhibit an array of proteinases that play significant roles in lung injury. Based on their localization, regulation and biochemical properties, we hypothesize that ov-serpins are ideally localized in the lung tissue and inflammatory cells to regulate the activity of proteinases released during inflammation, such as occurs in BPD. Transcriptional or post-translational alterations in ov-serpin expression in the immature lung can be associated with unopposed proteinase activity and thus, increased susceptibility to BPD. In order to investigate our hypothesis, we propose to utilize the well-characterized baboon models of BPD. The specific aims of this project are to: 1) correlate ov-serpin mRNA and protein expression in baboon lungs with the development of BPD by quantitative RT-PCR, immunoblotting, and immunohistochemistry, 2) characterize the activity of serine- and cysteine proteinases as ov-serpin targets in the airways of baboons with and without BPD by kinetic assays and identify in vivo target proteinases of ov-serpins by analyzing tracheal aspirate fluids by co-immunoprecipitation and nano-capillary HPLC-ion trap mass spectrometry (LC-MS/MS), 3) determine whether administration of recombinant SCCA1 (SERPINB3) alters the development of BPD in baboon models by monitoring clinical and biochemical parameters, and lung histopathology. These studies will enhance our understanding of the cellular and molecular mechanisms underlying BPD and facilitate development of novel preventive and therapeutic strategies for BPD.